Meaning of "$$"

Hello All,

I can't seem to find any documentation on what the "$$" at the beginning and end of a function.  Obviously, it seems like a delimiter, but I have seen examples such as where it has a string value between the $.  Why? What does this do?  I've done some searching and reading and can't quit figure it out.  

thanks,

Please see the following for the 8.3 online documentation:

CREATE FUNCTION emp_stamp() RETURNS trigger AS $emp_stamp$ <----note!
BEGIN
-- Check that empname and salary are given
IF NEW.empname IS NULL THEN
RAISE EXCEPTION 'empname cannot be null';
END IF;
IF NEW.salary IS NULL THEN
RAISE EXCEPTION '% cannot have null salary', NEW.empname;
END IF;

-- Who works for us when she must pay for it?
IF NEW.salary < 0 THEN
RAISE EXCEPTION '% cannot have a negative salary', NEW.empname;
END IF;

-- Remember who changed the payroll when
NEW.last_date := current_timestamp;
NEW.last_user := current_user;
RETURN NEW;
END;
$emp_stamp$ LANGUAGE plpgsql;